The present invention relates to detection and monitoring equipment for fluid pollution, including smoke and air pollution by light scatter techniques.
Devices are known for the detection of smoke by light scatter techniques. Such devices include a light source configured to irradiate through a volume of air provided in a sampling region in which smoke, dust or like particles may be suspended. Light scattered off said particles is collected on a light detector means. The amplitude of the signal from said light detector is an indication of the quantity of particulates in the fluid.
Particularly sensitive versions of such detectors are capable of monitoring low levels of fluid pollution and thus may be a useful tool for monitoring general atmospheric pollution. Such high sensitivity enables detection of fires at the earliest possible (incipient) stage, whereby the fire may be controlled by local personnel using portable extinguishers or by removal of the source of heat (e.g. by disconnection of electric current) before smoke levels become dangerous to life. Such detectors require a sensitivity as high as twenty micrograms of wood smoke per cubic meter for example, which is equivalent to a visual range of 40 kilometers.
The monitors disclosed in my earlier Australian Patent Specification Nos. 31843/84, 31842/84, 34537/84, 31841/84 and 42298/85 were developed primarily to detect the very earliest traces of smoke from overheating substances before fire develops. This has nowadays become a critical requirement because of the widespread use of synthetic materials in furniture and furnishings, wiring and equipment. Synthetic materials burn more fiercely and produce toxic fumes at rates considerably higher than their outmoded natural counterparts. Very early detection of smouldering has become vital to the preservation of life (e.g. dormitories) and valuable equipment (e.g. computers).
This prior apparatus can and does summon human intervention before smoke levels become dangerous to life or delicate equipment, it can cause an orderly shutdown of power supplies so that equipment overheating will subside (thereby preventing a fire), or it can operate automatic fire suppression and personnel evacuation systems.
The prior art utilizes a sampling chamber as described in Australian Specification No. 31843/84 through which a representative sample of air within the zone to be monitored, is continuously drawn by an aspirator. The air sample is normally irradiated by an intense, wideband light pulse from a Xenon lamp. A minuscule proportion of the incident photons are scattered off airborne particles towards a very sensitive detector, to produce an analog signal which, after signal processing, represents the level of pollution (smoke) present in the air. The instrument is so sensitive that photons scattered off air molecules alone are detected. Therefore, minor pollution is readily detected as an increased signal. Despite the greater sensitivity of the known apparatus the rate of false alarms is much lower than for conventional smoke detectors (which are comparatively insensitive, by two or three orders of magnitude).
British Specification No. 2045456 (Kallander) discloses a device for detecting the presence of suspended particles in a gas wherein a collimated light beam is directed through a measuring chamber, the chamber including an internally reflecting elliptical cylindrical reflector, the light beam coinciding with one focal axis and a light detector being arranged on the other focal axis. A radiation trap for the unscattered light beam is also disclosed.
Japanese Specification no. 6093944 (Okuda) discloses a detector not having a lens in which laser beam light crosses a small diameter specimen stream at right angles to a first parabolic surface mirror with a photoelectric converter (detector) provided at the focus of a second parabolic surface mirror.
The Okuda reference provides for a double reflection of the scattered light, thereby requiring careful optical alignment but leading to difficulty in achieving optical gain and maintaining alignment in use, particularly where the device is destined for use in vibrating and temperature variable environments.
Furthermore, Okuda is silent in respect of the cone angle within which scattered light emanates from the specimen stream and reflected onto to the detector cell.
U.S. Pat. No. 4,426,640 (Becconsall) discloses a pollution monitoring device using two laser beams of different wave lengths.
Japanese Specification no. 57.69230 (Mino) discloses a smoke detector in which light beams are transmitted to a smoke chamber through optical fibres.